This renewal application requests continued support of our post-doctoral training program in Pediatric Infectious Diseases at Columbia University Medical Center. Pediatric Infectious Diseases continues to be a critically important discipline as it seeks to increase our understanding of the pathogenesis and treatment of infectious diseases in infants, children, and adolescents. Our program has been funded since 1998 and has graduated 14 physicians in pediatric ID, all of whom are now engaged in academic endeavors. Three additional post-doctoral trainees are currently in training. Our trainees have performed basic, translational, clinical, and epidemiologic research in host-pathogen interactions; virulence factors; emerging pathogens; molecular epidemiology; safety and efficacy of vaccines; antimicrobial resistance and antimicrobial stewardship; and healthcare-associated infections. The objective of our program continues to be to train physician-scientists for careers in basic, translational, clinical, and epidemiologic research in academic settings and/or in the public health sector. In this proposed project period the research activities of the training program will reflect three complementary areas of research related to host-pathogen interactions which will include: bacterial/ viral pathogenesis; safety and effectiveness of vaccines; and public health and healthcare delivery. Thus, the faculty mentors described on this training grant are highly interdisciplinary and reflect the outstanding academic resources available at Columbia University Medical Center. Our faculty mentors are from the Departments of Pediatrics, Medicine, Microbiology & Immunology, Pathology & Cell Biology, Obstetrics & Gynecology, Pharmacology, and Psychiatry as well as the School of Nursing and the Mailman School of Public Health. Our training program in Pediatric Infectious Diseases lasts for 3 years. In this renewal application, we are requesting 5 more years of funding for 3 post-doctoral fellow trainees per year: one 1st year, one 2nd year, and one 3rd year trainee each year. During the 3-year program, the trainees engage in scholarly research guided by an experienced mentor. The trainees also acquire clinical expertise in Pediatric Infectious Diseases and are eligible to be board certified in this discipline at the end of their training. Thanks to this training grant and he strong program we have developed, we continue to recruit outstanding applicants who have completed their pediatric residencies, seek to develop their research skills in Pediatric Infectiou Diseases, and have the goal of pursuing academic endeavors in university or public health settings upon completion of their training.